Spinel
- Magnesium
- Magnesian spinel
The spinel is a common mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the cubic crystal system with the idealized chemical composition MgAl2O4 and is therefore chemically seen a magnesium aluminate. The spinel structure is one of the most important and frequent structural types.
Spinel developed predominantly octahedral, dodecahedral and rarely cubical crystals and twins, which can be up to 30 inches tall. But he also comes in the form of granular ago to massive mineral aggregates. Due to mixed crystal formation and frequent foreign admixtures of various metal ions such as iron, chromium, zinc, cobalt, or manganese are natural spinels from wide range of colors. As clear and transparent spinels also on polished surfaces have a strong, glass-like shine and due to their large Mohs hardness 7.5 to 8 are relatively insensitive to damage include these so-called " precious spinels " to the precious stones.
Many color varieties are now produced synthetically and used in addition to the use as a gemstone and as a raw material for technical ceramics and pigments such as Thénards blue as synthetic Cobaltspinell.
Etymology and history
The name origin is not fully understood. However, it is believed that he was originally from the ancient Greek σπίν ( ν ) ος [ Spin (n ) os] for " spark" or " sparkle " comes and thus indicates its luster or in relation to the typical spike-like, sharp-edged Kristalloktaeder has developed from the Latin spina, spinus or spinula for " thorn" or " pin " or spin ella for " Dörnchen " or "little thorn".
The name spinel is preserved in various spellings in Europe since at least the 16th century, so among other things as Spynell in England ( 1528), as Georgius Agricola by Spinella ( 1546) and as Spinellus by Anselm Boetius de Boodt (1609 ). Similar to the well-known since ancient name carbuncle carbuncle or spinel but not designated specifically known today as Magnesio or Edelspinell mineral, but generally red gems in every shade of crimson on red-violet ( Hyazinthfarben ) to yellowish white or whitish. Only in 1800 was recognized on the one hand, that the red ruby and the sapphire blue form only color varieties of the same mineral corundum and on the other hand, the spinel and the color and crystallographically similar minerals of the garnet group its own mineral species and learned to distinguish them.
Classification
Already in the outdated, but partly still in use 8th edition of the mineral classification by Strunz was part of the spinel to the mineral class of " oxides and hydroxides " and then to the Department of " oxides with molar ratio of metal: oxygen = 3: 4 ( spinel M3O4 and related compounds ) "where he along with gahnite, hercynite galaxite and the group of". aluminate spinels "with the system no IV/B.01 formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the spinel also in the department of " oxides with the molar ratio of metal: oxygen = 3: 4 and comparable " one. However, this is further divided according to the relative size of the cations involved, so that the mineral is "With only medium-sized cations " to find according to its composition in the subdivision where it is named as the " spinel " with the system no. 4.BB.05 and the other members Brunogeierit, chromite, Cochromit, Coulsonit, Cuprospinell, Filipstadit, Franklinite, gahnite, galaxite, hercynite, Jakobsit, Magnesiochromite, Magnesiocoulsonit, Magnesioferrit, magnetite, Manganochromit, Nichromit, Qandilit, Trevorit, Ulvöspinell, Vuorelainenit and Zincochromit forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the spinel into the class of " oxides and hydroxides " and there in the department of " multiple oxides ". Here he is with galaxite, hercynite and gahnite in the " aluminum sub- group " 07:02:01 within the subdivision " Multiple oxides ( A B2 ) 2X4, spinel group " to find.
Modifications and varieties
Pure spinel is colorless. However, the stoichiometry of the chemical formula is variable within wide limits, ie, magnesium, or aluminum may be present in different proportions or be replaced by actually formulaic foreign cations. Particularly large excesses of aluminum cations can be dissolved in it. An excess magnesium is possible only at extremely high temperatures (from about 1500 ° C).
This results in a wide range of possible colors ranging from purple to red to pink, yellow and from green to blue to brown to black. Some color varieties were given their own names and are also in the gemstone trade spread.
- "Noble Spinel " or " Rubinspinell " gets its powerful light to dark red color by diadochi replacement of Al2O3 by traces of Cr2O3. " Almandinspinell " is derived from the 19th century term for dark red spinels with a tinge of blue or violet.
- " Balas Ruby " or " Balasrubin " is an obsolete term for a pink to pale red gem, which spread around 1200 AD and served as a demarcation for a " carbuncle " or Rubin of inferior beauty. Since this title is misleading, it is now rejected by the CIBJO and in the gem trade as opposed to the alternative name " Balas Spinel " barely still in use.
- " Rubicell " or " Rubacell " as a diminutive form of the French rubis or Rubace ( Rubin) are to refer to yellow-orange to yellow-red, hyazinthähnliche varieties in use since the 17th century.
- Blue spinel or " Saphirspinell " gets its blue color by replacement of MgO by FeO up to 3.5%.
- When green spinel or " Chlorospinell " ( from Ancient Greek χλωρός chloros " light green, fresh", according to Gustav Rose, 1840 ) are parts of MgO and Al2O3 by traces of CuO and Fe2O3 by up to 15% replaced. " Chromium spinel " or " picotite " is a dark green by partial replacement of magnesium by iron and aluminum by chromium and iron to black spinel.
- " Pleonaste " (after René -Just Haiiy ), also Ceylanit ( after Jean -Claude Delamétherie 1793), is replaced by larger additions of FeO and Fe2O3 its brown to black color. Mostly he is also the opaque.
Pink Spinel on Pyrrhotite from Kuch -i - Lal, district Ishkashim, Tajikistan (size: 2.2 cm × 1.6 cm × 1.2 cm)
Sky Blue Spinel from Helena (Montana ), USA ( total size: 2.6 cm × 1.8 cm × 1.8 cm)
Purple Spinel from Ladjuar Medam, Sar -e -Sang, Badakhshan, Afghanistan (size: 4.5 cm × 4.0 cm × 3.7 cm)
Black spinel from Franklin ( New Jersey ), USA ( size 2.4 cm × 2.3 cm × 1.8 cm)
Education and Locations
Spinel forms as an ancillary part in ultrabasic rocks of the upper mantle as basalt and peridotite. It can also kontaktmetasomatisch by displacement of dolomite and limestone or kontaktmetamorph in gneiss and marble occur. In the rocks in question spinel usually takes the form of ingrown, well-trained, octahedral crystals and rare as a twin. In addition, it comes rolled out flat, more or less loose form also available in gemstone soaps. Accompanying minerals include andalusite, Chondrodite, forsterite, corundum, phlogopite, scapolite and sillimanite.
As a frequent mineral formation spinels are found in many localities, where so far (as of 2014) about 1600 localities as are known. The world's largest ever known spinel crystals has a reddish-purple red, flat twin with 17.8 cm diameter, which was found in 2005 in An Phu in the mining area Yên Luc in Vietnamese Yen Bai.
Known due to exceptional Spinellfunde also the Siberian Aldanhochland with Crystal finds the variety pleonaste of up to 15 cm in size was. At Amity and Sterling Hill (New Jersey) in the U.S. to 14 kg and 12 cm large crystals were found. Ratnapura were also known in Sri Lanka and Mogok in Myanmar, as well as Kukh -i - Lal (Tajikistan) in the Pamir Mountains for their purple and red crystal gemstone discoveries of particularly high quality and sizes of 2-5 cm. Particularly rare are the black and gray blue to purple star spinels with four - and sechsstrahligem asterism, which have been found mainly in Sri Lanka.
In Germany the mineral previously occurred in several quarries near Bötzingen, Horben, Immendingen, Schelingen, Scharnhausen and the cat's back in Baden- Württemberg; in many places in the Franconian Forest and Lower Bavaria; in high- cities and Kilsbach in Hesse; at several points Fund in the area of Bad Harzburg in Lower Saxony; in the Seven Mountains of North Rhine -Westphalia; in many places in the Eifel region of Rhineland -Palatinate; at Waldheim, Dresden, Hinterhermsdorf, Poehla ( Black Mountain ) and on to the Greifensteine and on Löbauer mountain in Saxony and at the crest of the mountain at Joldelund in Schleswig -Holstein.
In Austria one knows spinel among others Lölling and Kollnitz (municipality Sankt Paul in the Lavant Valley ) in Carinthia; from several locations in Dunkelsteinerwald and in the Waldviertel in Lower Austria; Dead head ( Hohe Tauern ) in Salzburg; from Stradner Kogel, from a quarry near Kloch, the " width- pit " at Hochlantsch and from a quarry near room in Styria; a slag heap near St. Gertraudi in Tyrol, as well as several places in Upper Austria Upper Austria.
In Switzerland, the mineral found so far mainly in the cantons Graubründen, Ticino and Valais.
Other localities lie include Afghanistan, Albania, Algeria, Antarctic, Argentina, Azerbaijan, Australia, Belgium, Bolivia, Bosnia and Herzegovina, Botswana, Brazil, Bulgaria, China, the Democratic Republic of Congo ( Zaire), in Fiji, Finland, France, French Guiana, and French Polynesia, Greece, Greenland, India, Iran, Iraq, Ireland, Israel, Italy, Japan, Yemen, Cambodia, Canada, Kazakhstan, Kenya, Lesotho, Libya, Madagascar, Malawi, Morocco, Mexico, Namibia, Nepal, Netherlands, New Caledonia, New Zealand, Nigeria, North Korea, Norway, Oman, Pakistan, Palestine, Papua New Guinea, Peru, Poland, Romania, Russia, Sweden, Zimbabwe, Slovakia, Spain, South Africa, Sudan, Suriname, Taiwan, Tanzania, Thailand, Turkey, Uganda, Ukraine, Hungary, Uzbekistan, Venezuela, the United Kingdom ( UK), the United States of America ( USA) and the Central African Republic.
Even in rock samples from the East Pacific Rise ( ultramafic complex " Hess- depth" ) and outside the Earth in comet dust from Wild 2 and in rock samples from the moon, brought the Apollo 14 and Apollo 16 missions, spinel could be detected.
Crystal structure
Spinel crystallizes isotypic with magnetite in the cubic crystal system in the space group Fd3m ( Raumgruppen-Nr. 227 ) with the lattice parameters a = 8.09 Å, and eight formula units per unit cell.
Use as a gemstone
Flawless spinels are coveted but rare gemstones. Red spinels in this case have a superficial resemblance to rubies. So, for example, noted the long held for a ruby "Black Prince's Ruby" ( Ruby the Black Prince ) in the Imperial State Crown and " Timur Ruby" in a necklace of the British Crown Jewels as well as some drop-shaped gems in the Wittelsbach crown of 1830 out as spinels.
Large and famous spinels
Manipulation and imitation
Natural spinels are generally fired to improve the color. Possible cracks in the rock are filled with various methods to increase its transparency.
Synthetic spinels for the jewelery industry have been manufactured since the 1920s by the Verneuil method in which aluminum oxide ( corundum, Al2O3) and magnesia ( periclase, MgO ) respond to spinel ( MgAl2O4 ). Using other additives can be generated as, among others, Co2O3 for blue and Ni2O3 for light green spinels, for example, aquamarine, garnet, ruby, sapphire, emerald, various tourmalines and even to imitate Moonstone each desired color varieties. Since the 1950 Lapis Lazuli can also be mimicked by synthetic sintered spinel.
Under the polarizing microscope, synthetic spinels show, however, always a typical abnormal stress birefringence and can thereby be distinguished from natural spinels.
Further use
Due to its high hardness and chemical resistance as well as its high melting point of 2135 ° C synthetic spinels for refractory and gas-tight technical ceramics are used.